Patent Document 1 discloses a technology of accurately processing the side of protrusion of a hub by the inventor. According to this technology, for a hub for Oldham coupling in which a linear protrusion is formed and coupled with a linear depression formed in a plane slider, the hub for Oldham coupling is formed with sintered alloy and is processed by pressing both sides of the protrusion like a sandwich. The slider uses a resin material such as a super engineering plastic or a conventional plastic and contains reinforcing agents such as glass, carbon or others, and thus it is described that the strength has been secured.    [PATENT DOCUMENT 1] JPA2006-29400